WO2010053116A1

WO2010053116A1 - Spark plug and manufacturing method therefor

Info

Publication number: WO2010053116A1
Application number: PCT/JP2009/068894
Authority: WO
Inventors: 鈴木　隆博; 加藤　友聡
Original assignee: 日本特殊陶業株式会社
Priority date: 2008-11-06
Filing date: 2009-11-05
Publication date: 2010-05-14
Also published as: EP2346125B1; US8344605B2; JP5331111B2; EP2346125A1; KR20110093767A; EP2346125A4; US20110210659A1; JPWO2010053116A1; CN102204043B; CN102204043A

Abstract

Disclosed are a spark plug with which the occurrence of blow-outs and the like can be suppressed and the ignition ability can be improved; and a manufacturing method therefor. A convex part (28) which opposes a center electrode (5) is formed in the contact electrode (27) of a spark plug. A precious metal chip (32) is provided in the center of the tip face of the convex part (28), and a ring-shaped fusion part (33) is provided abutting the perimeter of the precious metal chip (32); in addition, on the outer perimeter thereof a ring-shaped electrode parent material surface is provided. In addition, a spark discharge gap (35) is formed in the interval between the central electrode (5) and the tip of the convex part (28) containing the precious metal chip (32).

Description

Spark plug and manufacturing method thereof

The present invention relates to a spark plug used for an internal combustion engine such as an automobile engine and a method for manufacturing the same.

In general, a spark plug used in an internal combustion engine such as an automobile engine generates a spark discharge in a spark discharge gap between a center electrode and a ground electrode, thereby generating an air-fuel mixture supplied to a combustion chamber of the internal combustion engine. It is configured to ignite.

In recent years, internal combustion engines such as lean burn engines, direct injection engines, and low exhaust gas engines have been actively developed from the viewpoint of complying with exhaust gas regulations and improving fuel efficiency. In such an internal combustion engine, in order to ignite the air-fuel mixture, a spark plug having higher ignitability than before is required.

As a spark plug with improved ignitability, one having a convex portion on the ground electrode side is known.

For example, with respect to the electrode base material of the ground electrode formed of a nickel alloy or the like, a convex part is formed by welding a precious metal tip such as an iridium alloy or a platinum alloy that is excellent in spark wear resistance and oxidation wear resistance, Instead of the noble metal tip, there is known one in which a projection is formed by processing the electrode base material itself of the ground electrode (see, for example, Patent Document 1).

JP 2006-286469 A

However, on the internal combustion engine side, in order to improve ignitability, a high swirl type in which the flow rate of the air-fuel mixture in the combustion chamber is increased is increasing. In such an internal combustion engine, there is a high risk of occurrence of problems such as so-called blow-off, in which a spark generated in the spark discharge gap is blown away and misfires.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a spark plug capable of suppressing the occurrence of blow-off and the like and improving the ignitability, and a method for manufacturing the same.

Hereafter, each configuration suitable for solving the above-mentioned problems will be described in terms of items. In addition, the effect etc. peculiar to the structure which respond | corresponds as needed are added.

Configuration 1. The spark plug of this configuration has a center electrode that extends in the axial direction, an insulator that holds the center electrode, a metal shell that holds the insulator, and a base end of the metal shell that is joined to the tip of the metal shell. A ground electrode that is bent and fixed so that an inner surface of its own tip faces the tip of the center electrode, and a noble metal tip bonded to the inner surface of the ground electrode, the center electrode and the A spark plug in which a spark discharge gap is formed between the noble metal tip of the ground electrode,
The inner surface of the ground electrode is formed of a columnar convex portion made of an electrode base material of the ground electrode mainly composed of nickel and projecting along the axial direction,
The noble metal tip having a cross-sectional area smaller than the area of the tip surface of the convex portion is joined to the tip surface of the convex portion, and at least part of the periphery of the noble metal tip from the electrode base material of the ground electrode A discharge permissible surface is formed,
An interval of the spark discharge gap, which is a distance from the discharge surface of the central electrode in the axial direction to the discharge surface of the noble metal tip of the ground electrode, is 0.8 mm or more;
The protruding dimension of the noble metal tip of the ground electrode, which is the distance from the discharge surface of the noble metal tip of the ground electrode in the axial direction to the inner surface of the ground electrode, is 0.5 mm or more,
When the discharge surface of the center electrode and the discharge surface of the noble metal tip of the ground electrode are projected on a plane perpendicular to the axial direction, the center electrode is outside the region of the projected image of the discharge surface of the noble metal tip of the ground electrode. The projected image of the discharge surface does not protrude.

According to the above configuration 1, the noble metal tip mainly constituting the discharge surface is joined to the front end surface of the convex portion formed on the ground electrode, and the electrode matrix mainly composed of nickel is disposed around the noble metal tip. A discharge allowable surface made of a material is formed.

As a result, the discharge is normally performed between the center electrode and the noble metal tip of the ground electrode, but when a spark is caused by the influence of swirl or the like, the discharge permissible surface (nickel) around the noble metal tip The base material portion) functions as a discharge surface, and discharge is maintained.

Nickel alloys that serve as electrode base materials are more likely to oxidize than noble metals such as iridium and platinum constituting noble metal tips. For this reason, as the spark plug is used, an oxide film is formed on the surface of the electrode base material by being exposed to a high temperature atmosphere in the combustion chamber. In general, metal oxides have a smaller work function than noble metals such as iridium and platinum, so when discharge occurs in the electrode base material where the oxide film is formed, the discharge is likely to be maintained. It is done.

As a result, it is possible to improve the ignitability by suppressing the occurrence of blowout while suppressing the decrease in the durability of the electrode using the noble metal tip.

However, when the discharge surface of the center electrode and the discharge surface of the noble metal tip of the ground electrode are projected on a plane orthogonal to the axial direction, the discharge surface of the center electrode is outside the region of the projected image of the discharge surface of the noble metal tip of the ground electrode. In the configuration in which the projected image protrudes, a spark tends to fly to the discharge permissible surface (nickel base material portion), and the durability may be reduced. That is, the meaning of providing a noble metal tip for improving durability is reduced.

On the other hand, when the configuration in which the projection image of the discharge surface of the center electrode does not protrude outside the region of the projection image of the discharge surface of the noble metal tip of the ground electrode as in the present configuration 1, there is no influence of swirl or the like. Below, a discharge is performed between the center electrode and the noble metal tip of the ground electrode, and when a spark is caused by a swirl or the like, the discharge is maintained on the discharge permissible surface. As a result, it is possible to suppress flying to the discharge permissible surface and suppress a decrease in durability.

Also, in a spark plug having a configuration in which the spark discharge gap interval is less than 0.8 mm or a configuration in which the protruding dimension of the noble metal tip of the ground electrode is less than 0.5 mm, the above-mentioned problems such as blow-off are unlikely to occur. Therefore, the above-described operational effect of Configuration 1 is more effective in the spark plug in which the spark discharge gap interval is 0.8 mm or more and the protruding dimension of the noble metal tip is 0.5 mm or more.

Here, “main component” refers to the component having the highest mass ratio in the material (hereinafter the same).

When the noble metal tip is laser welded to the convex portion, a melted portion is formed around the noble metal tip. This melted portion is formed by melting the electrode base material of the ground electrode and the noble metal tip. Therefore, it is not included in the “discharge allowable surface made of the electrode base material of the ground electrode”.

On the other hand, when the noble metal tip is resistance-welded to the convex portion, a welding sag is formed around the noble metal tip so that the surface of the electrode base material is pushed away by the noble metal tip during the welding. Since it has the same component composition as that of the electrode base material, it may be included in the “discharge allowable surface made of the electrode base material of the ground electrode”.

Configuration 2. The spark plug of this configuration is the above-described configuration 1,
A chamfered portion is formed at an edge of the discharge allowable surface.

Examples of the chamfered portion include a curved R chamfered portion and a tapered C chamfered portion.

According to the configuration 2, the edge of the discharge permissible surface, that is, the corner formed by the tip surface and the side surface of the convex portion is chamfered, and the chamfered portion is formed, so that the blow-off at the corner is prevented. Occurrence can be suppressed. As a result, the effect of the said structure 1 can be improved more.

Configuration 3. The spark plug of this configuration is the

above configuration

1 or 2,
The discharge allowable surface is formed over the entire circumference of the noble metal tip.

According to the above-described configuration 3, since the discharge permissible surface is formed around the entire periphery of the noble metal tip, the discharge is reliably maintained regardless of the direction in which the spark is caused to flow by a swirl or the like.

Configuration 4. The spark plug of this configuration is any one of the above configurations 1 to 3,
The minimum distance between the outer periphery of the convex portion and the outer periphery of the noble metal tip is 0.1 mm or more and 0.5 mm or less.

Even if the cross-sectional area of the noble metal tip is set smaller than the area of the tip end surface of the convex portion, when the minimum distance between the outer circumferences of both is less than 0.1 mm and the area of the discharge permissible surface is small, the operation of the above configuration 1 It may be difficult to obtain an effect. Further, if the minimum distance between the outer peripheries of both exceeds 0.5 mm and the area of the discharge permissible surface becomes large, the ignitability and workability may be reduced. In view of this, by adopting the above-described configuration 4, it is possible to prevent the occurrence of such inconveniences and more reliably achieve the operational effects of the above-described configuration 1.

Configuration 5. The spark plug of this configuration is any one of the above configurations 1 to 4,
The protruding dimension of the noble metal tip from the front end surface of the convex portion in the axial direction is 0 mm or more and 0.2 mm or less.

When the protruding dimension of the noble metal tip is less than 0 mm, that is, when the noble metal tip is recessed from the tip surface of the convex portion, the distance between the center electrode and the discharge permissible surface around the noble metal tip is the distance between the center electrode and the noble metal tip. Since the distance is smaller than the distance, it is easy for the spark to fly to the discharge permissible surface, and the durability may be reduced. That is, the meaning of providing a noble metal tip for improving durability is reduced. In addition, when the protruding dimension becomes larger than 0.2 mm, the risk of blown out increases as in the conventional case. In view of this, it is preferable to use the above-described configuration 5 in order to maintain discharge on the discharge permissible surface when discharge is normally performed on the noble metal tip and a spark is caused by swirl or the like. . As a result, the effect of the said structure 1 is show | played more reliably.

Configuration 6. The spark plug of this configuration is any one of the above configurations 1 to 5,
A hole is formed at a position corresponding to the convex portion on the outer surface opposite to the inner surface of the ground electrode with respect to the axial direction.

Configuration 7. The spark plug manufacturing method of the present configuration includes a center electrode extending in the axial direction, an insulator holding the center electrode, a metal shell holding the insulator, and a base end portion of the metal shell at the distal end of the metal shell Are joined, bent, and fixed so that the inner surface of the tip portion thereof faces the tip portion of the center electrode, a columnar protrusion provided on the inner surface of the ground electrode, and the protrusion A spark plug gap is formed between the center electrode and the noble metal tip of the ground electrode and the tip end surface of the convex portion. ,
A welding step of welding the noble metal tip to the base of the ground electrode formed in a substantially straight rod shape;
An extruding step of forming the convex portion by extruding from a side opposite to the side where the noble metal tip is welded to a range in which at least the noble metal tip is included in the base of the ground electrode;
A bending step of forming the spark discharge gap by bending the base of the ground electrode so that the tip surface of the convex portion including the noble metal tip faces the tip of the center electrode. It is characterized by.

According to the configuration 7, the welding process is relatively easy by welding the noble metal tip before forming the convex portion. Furthermore, it becomes easy to ensure the desired protrusion amount of a convex part by forming a convex part by an extrusion process.

It is a partially broken front view which shows the whole spark plug of this embodiment. It is the partially broken enlarged view which expanded the principal part near the front-end | tip part (a center electrode and a ground electrode) of a spark plug. It is the schematic diagram which looked at the convex part of the ground electrode from the center electrode side to the axial direction. It is a cross-sectional schematic diagram which shows the convex part vicinity of a ground electrode. It is the partially broken enlarged view which expanded the principal part vicinity of a center electrode and a ground electrode. It is a schematic diagram which shows the projection image of the noble metal tip of a center electrode and the noble metal tip of a ground electrode projected on the plane orthogonal to an axial direction. It is the partially broken enlarged view which expanded the principal part of the conventional center electrode and ground electrode vicinity. It is the schematic diagram which looked at the convex part of the ground electrode in another embodiment from the center electrode side in the axial direction. It is a cross-sectional schematic diagram which shows the convex part vicinity of the ground electrode in another embodiment. It is a cross-sectional schematic diagram which shows the convex part vicinity of the ground electrode in another embodiment.

Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a partially cutaway front view showing a spark plug 1. In FIG. 1, the axis C1 direction of the spark plug 1 is defined as the vertical direction in the drawing, the lower side is described as the front end side of the spark plug 1, and the upper side is described as the rear end side.

The spark plug 1 is composed of an insulator 2 as an elongated insulator, a cylindrical metal shell 3 that holds the insulator 2, and the like.

A shaft hole 4 is formed through the insulator 2 along the axis C1. A center electrode 5 is inserted and fixed on the front end side of the shaft hole 4, and a terminal electrode 6 is inserted and fixed on the rear end side. A resistor 7 is disposed between the center electrode 5 and the terminal electrode 6 in the shaft hole 4, and both ends of the resistor 7 are connected to the center electrode via conductive glass seal layers 8 and 9. 5 and the terminal electrode 6 are electrically connected to each other.

The center electrode 5 protrudes from the tip of the insulator 2 and the terminal electrode 6 is fixed in a state of protruding from the rear end of the insulator 2.

On the other hand, the insulator 2 is formed by firing alumina or the like, as is well known, and has a flange-shaped large-diameter portion 11 that protrudes radially outward at a substantially central portion in the direction of the axis C1 in its outer shape. And an inner body portion 12 having a smaller diameter on the distal end side than the large diameter portion 11, and an inner body portion 12 having a smaller diameter on the distal end side than the intermediate body portion 12, and an internal combustion engine (engine). And a leg length portion 13 exposed to the combustion chamber. Of the insulator 2, the distal end side including the large-diameter portion 11, the middle trunk portion 12, and the leg long portion 13 is accommodated in a metal shell 3 formed in a cylindrical shape. A step portion 14 is formed at the connecting portion between the leg long portion 13 and the middle trunk portion 12, and the insulator 2 is locked to the metal shell 3 at the step portion 14.

The metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and a screw portion (male screw portion) 15 for attaching the spark plug 1 to the engine head is formed on the outer peripheral surface thereof. A seat portion 16 is formed on the outer peripheral surface on the rear end side of the screw portion 15, and a ring-shaped gasket 18 is fitted on the screw neck 17 on the rear end of the screw portion 15. Further, on the rear end side of the metal shell 3, a tool engaging portion 19 having a hexagonal cross section for engaging a tool such as a wrench when the metal shell 3 is attached to the engine head is provided. A caulking portion 20 for holding the insulator 2 is provided.

Further, a step portion 21 for locking the insulator 2 is provided on the inner peripheral surface of the metal shell 3. The insulator 2 is inserted from the rear end side to the front end side of the metal shell 3, and the rear end of the metal shell 3 is engaged with the step portion 14 of the metal shell 3. It is fixed by caulking the opening on the side radially inward, that is, by forming the caulking portion 20. An annular plate packing 22 is interposed between the

step portions

14 and 21 of both the insulator 2 and the metal shell 3. Thereby, the airtightness in the combustion chamber is maintained, and the fuel air entering the gap between the leg long portion 13 of the insulator 2 exposed to the combustion chamber and the inner peripheral surface of the metal shell 3 is prevented from leaking outside.

Further, in order to make the sealing by caulking more complete,

annular ring members

23 and 24 are interposed between the metal shell 3 and the insulator 2 on the rear end side of the metal shell 3, and the

ring member

23 , 24 is filled with powder of talc (talc) 25. That is, the metal shell 3 holds the insulator 2 via the plate packing 22, the

ring members

23 and 24, and the talc 25.

A ground electrode 27 having a substantially L shape is joined to the front end surface 26 of the metal shell 3. That is, the ground electrode 27 is disposed so that the base end portion thereof is welded to the front end surface 26 of the metal shell 3, the front end side is bent back, and the inner side surface thereof faces the front end portion of the center electrode 5. Has been.

Here, the configuration of the center electrode 5 and the ground electrode 27 will be described in detail with reference to FIG. FIG. 2 is a partially broken enlarged view in which a main part in the vicinity of the tip part (the center electrode 5 and the ground electrode 27) of the spark plug 1 is enlarged.

The electrode base material of the center electrode 5 and the ground electrode 27 is made of a nickel (Ni) alloy containing nickel as a main component. However, a conductive core made of copper or a copper alloy is embedded in the center electrode 5 in order to increase thermal conductivity. Thereby, the center electrode 5 consists of the inner layer 5A which consists of copper or a copper alloy, and the outer layer 5B which consists of Ni alloy.

The center electrode 5 has a rod-like shape as a whole, and its tip side is reduced in diameter. A columnar noble metal tip 31 is joined to the tip of the center electrode 5 by resistance welding, laser welding, or the like.

Further, a convex portion 28 is formed on the inner side surface 27 a of the ground electrode 27 facing this so as to face the noble metal tip 31. The convex portion 28 protrudes from the inner side surface 27a of the ground electrode 27 toward the center electrode 5 side along the axis C1 direction, and the cross-sectional shape along the radial direction (left and right direction in FIG. 2) orthogonal to the axis C1 direction is substantially circular. It has a cylindrical shape. The convex portion 28 is formed by extrusion from the outer surface 27b of the ground electrode 27, as will be described later. Therefore, a bottomed hole portion 29 formed at the time of extrusion is opened on the outer surface 27 b of the ground electrode 27.

A cylindrical noble metal tip 32 is joined to the tip surface of the convex portion 28 by laser welding. The noble metal tip 32 is formed of a noble metal alloy mainly containing a noble metal such as iridium or platinum.

As shown in FIGS. 3 and 4, the cross-sectional area of the noble metal tip 32 is set smaller than the area of the tip surface of the convex portion 28. For this reason, the front end surface of the convex portion 28 is provided with a noble metal tip 32 in the center, and adjacent to the periphery of the noble metal tip 32, an annular molten portion 33 formed during laser welding, and an annular shape on the outer peripheral side thereof. And the electrode base material surface 28a. The electrode base material surface 28a constitutes a discharge permissible surface in the present embodiment. The electrode base material surface 28a in the present embodiment is formed over the entire circumference of the noble metal tip 32, and the radial width of the convex portion 28 (the outer periphery of the convex portion 28, the area including the noble metal tip 32 and the melting portion 33). Is set to be 0.1 mm or more and 0.5 mm or less.

Further, as shown in FIG. 4, the noble metal tip 32 is flush with the electrode base material surface 28a of the convex portion 28 or joined so as to protrude from the electrode base material surface 28a. In the present embodiment, the distance from the electrode base material surface 28a of the convex portion 28 to the discharge surface 32a of the noble metal tip 32 (the surface facing the noble metal tip 31 of the center electrode 5) in the direction of the axis C1, that is, the projected dimension of the noble metal tip 32. Y is set to be 0 mm or more and 0.2 mm or less.

Under the above configuration, a spark discharge gap 35 as a spark discharge gap is formed between the center electrode 5 and the convex portion 28. In a normal state, discharge is mainly performed between the

noble metal tips

31 and 32. On the other hand, when a spark flows due to the influence of swirl or the like, the electrode base material surface 28a around the noble metal tip 32 functions as a discharge surface. Then, the discharge is maintained.

As a result, according to the spark plug 1 having the above-described configuration, it is possible to suppress the occurrence of blow-off and the like and to improve the ignitability while suppressing a decrease in the durability of the ground electrode 27.

Next, a method for manufacturing the spark plug 1 configured as described above will be described. First, the metal shell 3 is processed in advance. That is, a cylindrical metal material (for example, an iron-based material such as S17C or S25C or a stainless steel material) is formed by forming a through-hole by cold forging to produce a rough shape. Thereafter, the outer shape is adjusted by cutting to obtain a metal shell intermediate.

Subsequently, a ground electrode 27 base is fabricated. More specifically, first, Ni alloy is cast and annealed to produce the ground electrode 27 base. For example, using a vacuum melting furnace, a Ni alloy melt is prepared, and after the ingot is prepared from each melt by vacuum casting or the like, the ingot is subjected to hot working, drawing, etc., to a predetermined dimension. And it processes to a shape and produces the ground electrode 27 original material.

Subsequently, the ground electrode 27 base material formed in this way is resistance-welded to the front end surface of the metal shell intermediate body. Thereafter, the threaded portion 15 is formed by rolling at a predetermined portion of the metal shell intermediate. Thereby, the metal shell 3 to which the ground electrode 27 base material is welded is obtained. The metal shell 3 to which the ground electrode 27 base material is welded is plated with zinc or nickel.

On the other hand, separately from the metal shell 3, the insulator 2 is molded. For example, by using a raw material powder mainly composed of alumina and containing a binder or the like, a green granulated material for molding is prepared, and rubber press molding is used to obtain a cylindrical molded body. The obtained molded body is ground and shaped. Then, the shaped one is put into a firing furnace and fired. The insulator 2 is obtained by performing various grinding | polishing processes after baking.

In addition, the center electrode 5 is manufactured separately from the metal shell 3 and the insulator 2. Here, the outer layer 5B made of a Ni alloy is forged, and an inner layer 5A made of copper or a copper alloy is provided at the center thereof. Further, a noble metal tip 31 is joined to the tip portion by resistance welding, laser welding or the like.

Then, the insulator 2 and the center electrode 5, the resistor 7, and the terminal electrode 6 obtained as described above are sealed and fixed by the glass seal layers 8 and 9. The glass seal layers 8 and 9 are generally prepared by mixing borosilicate glass and metal powder, and the prepared material is injected into the shaft hole 4 of the insulator 2 with the resistor 7 interposed therebetween. Then, after the terminal electrode 6 is pressed from the rear, it is baked and hardened in a firing furnace.

Thereafter, the insulator 2 including the center electrode 5 and the terminal electrode 6 respectively manufactured as described above and the metal shell 3 including the ground electrode 27 base body are assembled. More specifically, it is fixed by caulking the opening on the rear end side of the metal shell 3 formed relatively thin inward in the radial direction, that is, by forming the caulking portion 20.

Subsequently, a noble metal tip 32 is joined by laser welding to a predetermined portion of the ground electrode 27 base body in the metal shell 3 to which the insulator 2 is assembled. This process corresponds to the welding process in this embodiment.

When laser welding the noble metal tip 32, for example, the noble metal tip 32 is resistance-welded in advance to a predetermined portion of the ground electrode 27 base body, and laser light is irradiated around the resistance-welded noble metal tip 32. Thus, the noble metal tip 32 and the ground electrode 27 base are laser welded. For this reason, around the noble metal tip 32, a molten portion 33 is formed by melting the Ni alloy that is the electrode base material of the ground electrode 27 and the noble metal alloy that is a component of the noble metal tip 32 during the welding.

Then, the welded portion of the noble metal tip 32 is extruded from the opposite side of the ground electrode 27 base, and the convex portion 28 and the hole portion 29 are formed. This process corresponds to the extrusion process in this embodiment.

In order to produce such a ground electrode 27 base material, a method using a known extruder equipped with a punching tool capable of forming a hole can be employed.

As the extrusion machine, for example, a punch tool, a plate-like presser mold having a through-hole through which the punch tool passes, a groove-shaped storage section that stores the ground electrode 27 base body, and a storage section provided in the storage section are provided. An extruder or the like provided with a receiving die having a through hole and a presser die placed on the upper surface, and a receiving pin inserted into the through hole of the receiving die.

In order to extrude the ground electrode 27 base material using this extrusion processing machine, the presser die is overlaid and fixed on the upper surface of the receiving mold in which the ground electrode 27 base material is accommodated in the accommodating portion. A punching tool is pressed from the through hole to the ground electrode 27 base, whereby the convex portion 28 when the receiving electrode is used as the ground electrode 27 is pushed out while being received by the receiving pin. At this time, the shape and size of the hole 29 can be adjusted by adjusting the shape and size of the punch tool, and the shape and size of the through hole of the receiving mold and / or the receiving pin can be adjusted. Thus, the shape and size of the convex portion 28 can be adjusted.

Finally, the ground electrode 27 is bent so that the ground electrode 27 has a final shape, and a spark discharge gap 35 is formed. This process corresponds to the bending process in the present embodiment. At this time, the gap is adjusted between the noble metal tip 31 at the tip of the center electrode 5 and the tip surface of the convex portion 28 including the noble metal tip 32 on the ground electrode 27 side.

Thus, the spark plug 1 having the above-described configuration is manufactured through a series of steps.

Next, in order to confirm the effects achieved by the present embodiment, the width X of the electrode base material surface 28a (hereinafter simply referred to as the electrode base material width X) and the protruding dimension Y (hereinafter simply referred to as the noble metal tip 32) are described. Various samples with different chip protrusion dimensions Y) were prepared one by one, and a desktop spark discharge test was performed to perform various evaluations. The experimental results are described below.

Samples having electrode base material widths X set to 0 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, and 0.7 mm are group A to A, respectively. Group H, with respect to groups B to H, the tip protruding dimension Y is -0.1 mm (the discharge surface 32a of the noble metal tip 32 is recessed from the electrode base material surface 28a of the projection 28), 0 mm, 0. Samples set to 1 mm, 0.2 mm, 0.3 mm, and 0.4 mm were produced as Samples 1 to 6, respectively.

And, as a desktop spark discharge test, two types of tests were conducted: a spark flying performance test and a spark flying position confirmation test.

In the spark flying performance test, each sample was mounted in a chamber set in an atmospheric atmosphere of 0.4 MPa, and an air flow at a flow rate of 5.0 m / sec was applied between the spark discharge gaps 35, and 100 times each. A spark discharge was performed. And about each sample, the frequency | count of generation | occurrence | production of the blow-off (disconnection of discharge) was confirmed by the measurement of a video image and a discharge waveform, and the blow-off occurrence rate was verified. The evaluation results are shown in Table 1.

In Table 1, a case where the blow-off occurrence rate is less than 10% is rated as “◎” as being particularly excellent in the spark flying performance, and a case where the blow-off occurrence rate is 10% or more and less than 20% It was decided to give a rating of “◯” as being excellent in flying performance. On the other hand, those with a blowout occurrence rate of 20% or more were evaluated as “x” because there was a problem with the sparking performance. However, the evaluation shown in Table 1 shows a relative evaluation in this test, and even if the determination is impossible (x), it does not necessarily indicate that the product cannot be used.

As can be seen from Table 1, with regard to Group A in which the electrode base material width X is 0 mm, the blow-off occurrence rate is 28%, and the blow-off occurrence rate is extremely high compared to the other groups B to H. I understand. In addition, since the electrode base material width X is 0 mm, that is, the group A (see FIG. 7) that does not have the electrode base material surface 28a (discharge allowable surface) around the noble metal tip 32, it is irrelevant to the chip protruding dimension Y. In this spark flying performance test, only a sample having a noble metal tip 32 thickness of 0.3 mm (corresponding to a tip protruding dimension Y of 0.3 mm) was tested.

As for groups B to H, as can be seen by comparing samples 1 to 4 with

samples

5 and 6,

samples

5 and 6 having a tip protruding dimension Y of 0.3 mm or more have a high blow-off occurrence rate. It turns out that it becomes. This is considered because the gap of the spark discharge gap 35 from the center electrode 5 to the electrode base material surface 28a of the convex portion 28 is substantially increased.

Judging from the above results, it can be seen that the electrode base material width X is preferably set to 0.1 mm or more, and the tip protruding dimension Y is preferably set to 0.2 mm or less. Further, in the groups G and H in which the electrode base material width X is 0.6 mm or more, there is almost no difference between the samples 1 to 6 in the group F and the blowout occurrence rate. With respect to the upper limit, it is preferable that the upper limit is 0.5 mm or less in consideration of a decrease in ignitability and workability.

Further, in the spark flying position confirmation test, each sample was mounted in a chamber set in an atmospheric atmosphere of 0.4 MPa, and spark discharge was performed 100 times without applying an air flow. Then, for each sample, the spark spark position on the ground electrode 27 side was confirmed by a video image, and the spark rate on the discharge surface 32a of the noble metal tip 32 was verified. The evaluation results are shown in Table 2, Table 3, and Table 4. In Table 2, Table 3, and Table 4, only the samples 1 to 4 of the groups B, D, F, and H are shown for convenience.

Table 2 shows the evaluation results of the samples in which the diameter φ1 (see FIG. 5) of the noble metal tip 31 of the center electrode 5 is set to 0.8 mm and the diameter φ2 (see FIG. 5) of the noble metal tip 32 of the ground electrode 27 is set to 0.8 mm. Is shown.

Table 3 shows the evaluation results of the samples in which the diameter φ1 of the noble metal tip 31 of the center electrode 5 is set to 0.8 mm and the diameter φ2 of the noble metal tip 32 of the ground electrode 27 is set to 0.7 mm.

Table 4 shows the evaluation results of samples in which the diameter φ1 of the noble metal tip 31 of the center electrode 5 is set to 0.8 mm and the diameter φ2 of the noble metal tip 32 of the ground electrode 27 is set to 0.9 mm.

As can be seen from Table 2, with respect to sample 1 in which the chip protruding dimension Y is set to −0.1 mm, in each of the groups B, D, F, and H, the firing rate to the discharge surface 32a of the noble metal tip 32 is another sample. Extremely low compared to 2-4. That is, the flying ratio of the convex portion 28 to the electrode base material surface 28a is high. This is because if the discharge surface 32a of the noble metal tip 32 is in a position recessed from the electrode base material surface 28a of the convex portion 28, the center electrode 5 (noble metal tip 31) and the noble metal tip can be used even in a situation where there is no influence of swirl or the like. Since the distance from the electrode base material surface 28a around 32 is smaller than the distance between the center electrode 5 (the noble metal tip 31) and the discharge surface 32a of the noble metal tip 32, a spark is generated on the electrode base material surface 28a of the convex portion 28. This is thought to be easy to fly.

Therefore, considering that the Ni alloy as the electrode base material of the ground electrode 27 has lower durability than the noble metal tip 32, it is preferable to improve the durability by setting the tip protruding dimension Y to 0 mm or more. .

As can be seen by comparing the results shown in Table 2 and Table 3, when the diameter φ2 of the noble metal tip 32 of the ground electrode 27 is smaller than the diameter φ1 of the noble metal tip 31 of the center electrode 5, each group B, In each of the D, F, and H samples, the rate of fire on the discharge surface 32a of the noble metal tip 32 is extremely low. That is, the flying ratio of the convex portion 28 to the electrode base material surface 28a is high. This is probably because the area of the electrode base material surface 28a of the convex portion 28 facing the discharge surface 31a (see FIG. 5) of the noble metal tip 31 of the center electrode 5 in the direction of the axis C1 is large.

On the other hand, when the diameter φ2 of the noble metal tip 32 of the ground electrode 27 is larger than the diameter φ1 of the noble metal tip 31 of the center electrode 5, as can be seen by comparing the results shown in Table 2 and Table 4, both noble metals As in the case where the diameters φ1 and φ2 of the

chips

31 and 32 are the same, the samples of each group B, D, F, and H have a high rate of fire on the discharge surface 32a of the noble metal tip 32. In addition, when the diameter φ2 of the noble metal tip 32 of the ground electrode 27 is larger than the diameter φ1 of the noble metal tip 31 of the center electrode 5, and when the diameters φ1 and φ2 of both the

noble metal tips

31 and 32 are the same, they blow out. There is almost no difference in the incidence.

From the above results, as shown in FIG. 6, when the discharge surface 31a of the noble metal tip 31 of the center electrode 5 and the discharge surface 32a of the noble metal tip 32 of the ground electrode 27 are projected on a plane orthogonal to the direction of the axis C1, It can be seen that it is more preferable that the projected image 31x of the discharge surface 31a of the noble metal tip 31 of the center electrode 5 does not protrude outside the region of the projected image 32x of the discharge surface 32a of the noble metal tip 32 of the electrode 27.

Next, as a comparative example, in order to confirm the effects achieved by the present embodiment, a spark plug that does not have the electrode base material surface 28a (discharge permissible surface) around the noble metal tip 32 as shown in FIG. The distance from the inner surface 27a of the ground electrode 27 to the discharge surface 32a of the noble metal tip 32 in the direction of the axis C1, that is, the protrusion dimension Z of the noble metal tip 32 (hereinafter simply referred to as the chip protrusion dimension Z), and the distance between the spark discharge gaps 35 Various samples with different G (hereinafter, simply referred to as gap interval G) were produced one by one, and the same test was performed under the same conditions as the above-mentioned spark flying performance test, and the blow-off occurrence rate was verified. The evaluation results are shown in Table 5.

As samples, those having gap intervals G set to 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, and 1.1 mm are group J to group M, respectively, and the chip protrusion dimension Z is set for each group. Were prepared as Samples 1 to 5, respectively, having a thickness of 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, and 0.8 mm. In each sample, the diameter φ1 of the noble metal tip 31 of the center electrode 5 is set to 0.8 mm, and the diameter φ2 of the noble metal tip 32 of the ground electrode 27 is set to 0.8 mm.

In Table 5, the case where the blow-off occurrence rate was less than 20% was evaluated as “◯” because it was excellent in sparking performance. On the other hand, those with a blowout occurrence rate of 20% or more were evaluated as “x” because there was a problem with the sparking performance. However, the evaluation shown in Table 5 shows a relative evaluation in this test, and even if the determination is impossible (x), it does not necessarily indicate that the product cannot be used.

As can be seen from Table 5, regarding the groups J and K with the gap interval G being 0.6 mm and 0.7 mm, the blow-off occurrence rate is less than 20% in all the samples 1 to 5 having different chip protrusion dimensions Z. It can be seen that the occurrence rate of blow-out is low as compared with the other groups L, M, and N. That is, it can be seen that in a configuration where the gap interval G is less than 0.8 mm, it is difficult for blowout to occur.

For groups L, M, and N, as can be seen by comparing

samples

1 and 2 with samples 3 to 5, in

samples

1 and 2, the blow-off occurrence rate is less than 20%, and the chip protrusion dimension Z It can be seen that the occurrence rate of blow-off is lower than that of samples 3 to 5 having a thickness of 0.5 mm or more. In other words, it can be seen that in a configuration in which the chip protruding dimension Z is less than 0.5 mm, it is difficult for blowout to occur in the first place.

Judging from the above results, the gap gap G is 0.8 mm or more and the chip protruding dimension Z is 0.5 mm or more. Various functions and effects of this embodiment will be more effective.

In addition, it is not limited to the description content of embodiment mentioned above, For example, you may implement as follows.

(A) In the above embodiment, the width X of the electrode base material surface 28a of the convex portion 28 is set to be 0.1 mm or more and 0.5 mm or less. Not limited to this, at least the cross-sectional area of the noble metal tip 32 is set smaller than the area of the front end surface of the convex portion 28, and the electrode base material surface 28 a is formed around the noble metal tip 32 at the front end surface of the convex portion 28. It suffices if the configuration is as follows. However, as can be seen from the verification results, the width X of the electrode base material surface 28a is more preferably 0.1 mm or more and 0.5 mm or less.

(B) In the above embodiment, the protruding dimension Y of the noble metal tip 32 is set to be 0 mm or more and 0.2 mm or less, but the protruding dimension Y is not limited to this. However, as can be seen from the verification results, it is more preferable that the projected dimension Y is 0 mm or more and 0.2 mm or less.

(C) The

noble metal tips

31 and 32 in the above embodiment are formed of an iridium alloy or a platinum alloy. However, the present invention is not limited to this, and the

noble metal tips

31 and 32 may be formed of a noble metal alloy mainly composed of other noble metals. Good. Further, the noble metal tip 31 on the center electrode 5 side may be omitted, but it is preferable to provide the noble metal tip 31 also on the center electrode 5 side in terms of durability improvement.

(D) In the above embodiment, the noble metal tip 32 is joined to the ground electrode 27 by laser welding. However, the present invention is not limited thereto, and may be joined by other methods such as resistance welding. In the case of resistance welding, since the melted portion 33 is not formed, most of the portion excluding the noble metal tip 32 becomes the electrode base material surface 28a.

(E) The convex portion 28 and the noble metal tip 32 are not limited to the circular shape (cylindrical shape or cross-sectional circular tip) of the above-described embodiment, but are of different shapes, for example, a polygonal shape (a prismatic shape or a square tip). A thing may be adopted. For example, as shown in FIGS. 8 and 9, a quadrangular prism-shaped convex portion 28 that protrudes in the direction of the axis C1 (vertical direction in FIG. 9) along the distal end surface of the ground electrode 27 is formed at the distal end portion of the ground electrode 27. At the same time, the noble metal tip 32 having a quadrangular (rectangular) cross-sectional shape along the direction orthogonal to the direction of the axis C1 (the left-right direction in FIGS. 8 and 9) is provided on the tip surface of the convex portion 28 (upper side in FIG. 9). It is good also as a structure arrange | positioned along the front end surface of the ground electrode 27. FIG.

(F) In the above embodiment, the electrode base material surface 28a is formed over the entire circumference of the noble metal tip 32. However, the present invention is not limited to this, and as shown in FIGS. The electrode base material surface 28a may be formed in the part. However, if the electrode base material surface 28a is formed over the entire circumference of the noble metal tip 32, the discharge is reliably maintained regardless of the direction in which the spark is caused to flow by the swirl or the like. preferable.

(G) Not limited to the above embodiment, as shown in FIG. 10, the edge of the electrode base material surface 28a may be chamfered to provide a chamfered portion 28b. Further, in FIG. 10, a curved R chamfered portion is illustrated as the chamfered portion 28b. However, the present invention is not limited to this, and a tapered C chamfered portion may be employed.

Here, with respect to the samples 1 to 6 of the groups A to H in which the electrode base material width X and the chip protruding dimension Y are different, the blow-off in the case where the chamfered portion 28b is provided at the edge of the electrode base material surface 28a, respectively. The verification is performed for the occurrence rate and the blow-out occurrence rate when the chamfered portion 28b is not provided. Table 6 below shows the results of the same test performed for each sample under the same conditions as the spark performance test of the above embodiment.

In Table 6, a case where the blow-off occurrence rate is less than 10% is evaluated as “◎” as being particularly excellent in the spark flying performance, and a case where the blow-off occurrence rate is 10% or more and less than 20% It was decided to give a rating of “◯” as being excellent in flying performance. Table 6 shows only samples 4 to 6 of groups B, D, F, G, and H for convenience.

As can be seen from Table 6, in all the samples, it is found that the occurrence rate of blow-off can be reduced when the chamfered portion 28b is provided at the edge of the electrode base material surface 28a than when the chamfered portion 28b is not provided. This is considered to be due to the fact that the area of the discharge-acceptable surface capable of flying is substantially increased by forming the chamfered portion 28a.

DESCRIPTION OF SYMBOLS 1 ... Spark plug, 2 ... Insulator, 3 ... Main metal fitting, 5 ... Center electrode, 27 ... Ground electrode, 28 ... Convex part, 28a ... Electrode base material surface, 29 ... Hole part, 31, 32 ... Precious metal tip, 33 ... melted part, 35 ... spark discharge gap, C1 ... axis, X ... electrode base material width, Y ... chip protruding dimension.

Claims

A center electrode extending in the axial direction, an insulator that holds the center electrode, a metal shell that holds the insulator, and a base end portion of the metal shell that is joined to the distal end of the metal shell and bends A ground electrode fixed so that the inner side surface of the portion faces the tip of the center electrode, and a noble metal tip joined to the inner side surface of the ground electrode, and the center electrode and the noble metal tip of the ground electrode A spark plug in which a spark discharge gap is formed,
The inner surface of the ground electrode is formed of a columnar convex portion made of an electrode base material of the ground electrode mainly composed of nickel and projecting along the axial direction,
The noble metal tip having a cross-sectional area smaller than the area of the tip surface of the convex portion is joined to the tip surface of the convex portion, and at least part of the periphery of the noble metal tip from the electrode base material of the ground electrode A discharge permissible surface is formed,
An interval of the spark discharge gap, which is a distance from the discharge surface of the central electrode in the axial direction to the discharge surface of the noble metal tip of the ground electrode, is 0.8 mm or more;
The protruding dimension of the noble metal tip of the ground electrode, which is the distance from the discharge surface of the noble metal tip of the ground electrode in the axial direction to the inner surface of the ground electrode, is 0.5 mm or more,
When the discharge surface of the center electrode and the discharge surface of the noble metal tip of the ground electrode are projected on a plane orthogonal to the axial direction, the center electrode is outside the region of the projected image of the discharge surface of the noble metal tip of the ground electrode. A spark plug characterized in that a projected image of a discharge surface does not protrude.
The spark plug according to claim 1, wherein a chamfered portion is formed at an edge of the discharge permissible surface.
The spark plug according to claim 1 or 2, wherein the discharge permissible surface is formed over the entire circumference of the noble metal tip.
The spark plug according to any one of claims 1 to 3, wherein a minimum distance between an outer periphery of the convex portion and an outer periphery of the noble metal tip is 0.1 mm or more and 0.5 mm or less.
The spark plug according to any one of claims 1 to 4, wherein a protruding dimension of the noble metal tip from a tip surface of the convex portion in the axial direction is set to 0 mm or more and 0.2 mm or less.
6. A hole is formed at a position corresponding to the convex portion on an outer surface opposite to an inner surface of the ground electrode with respect to the axial direction. Spark plug.
A center electrode extending in the axial direction, an insulator that holds the center electrode, a metal shell that holds the insulator, and a base end portion of the metal shell that is joined to the front end of the metal shell and bent to have its tip A ground electrode fixed so that the inner surface of the portion faces the tip of the center electrode, a columnar protrusion provided on the inner surface of the ground electrode, and a noble metal tip bonded to the tip of the protrusion A spark plug manufacturing method in which a spark discharge gap is formed between the center electrode and the noble metal tip of the ground electrode and the tip surface of the convex part,
A welding step of welding the noble metal tip to the base of the ground electrode formed in a substantially straight rod shape;
An extruding step of forming the convex portion by extruding a range including at least the noble metal tip out of the ground electrode base material from a side opposite to the side where the noble metal tip is welded;
A bending step of forming the spark discharge gap by bending the base of the ground electrode so that the tip surface of the convex portion including the noble metal tip faces the tip of the center electrode. A method of manufacturing a spark plug characterized by